In order to meet the deceleration braking of a certain type of vehicle,through vehicle force analysis and matching calculation,the required braking torque of the hydraulic retarder in different gears and slopes was obtained.The Fluent software was used as a platform to numerically simulate the internal flow field of the hydraulic retarder,and the braking torque was solved based on the numerical solution of the flow field at different rotor speeds;the bench performance test of the hydraulic retarder was carried out,and the reliability of the simulation data was verified by performing a comparative analysis of the torque between the test data and simulation results.The results show that the required braking torque for a constant speed downhill increases with the increase of gears at the same slopes and increases with the increase of slopes at the same gears;with the increasing rotation speed of the rotor,the braking torque of the retarder increases,and at the maximum rotation speed of 2 100 r/min,the braking torque reaches 2 3083 Nm.The simulation values are generally consistent with the experimental values,demonstrating the accuracy of the simulation analysis.